In the related art, an electric tool includes a tool body driven by electric power, and a battery pack that serves as a power source for the tool body. The battery pack is configured to be detachably mounted to the tool body. The battery pack includes a housing case that forms an exterior cover, and a battery body that is installed in the housing case. The battery body includes a plurality of battery cells that can be charged and discharged, and a control board that controls the charge and discharge operations. Lead plates are connected to electrodes of the plurality of battery cells so that the battery cells are electrically connected in series or in parallel to each other.
Meanwhile, there may be an occasion that the afore-mentioned electric tool is used outdoors. Therefore, water such as raindrops may be splashed on such a battery pack, so that water may enter into the housing case. Here, when water enters into the housing case to cause the above-mentioned lead plates to be soaked in the water, unintended lead plates may be electrically connected to each other to the result that electricity, which is charged in battery cells, leaks.
For this reason, among battery packs, a battery pack has been known that is provided with a drain hole at a bottom portion of a housing case in order to discharge the water, which has been entered into the housing case, to the outside of the housing case (for example, see JP-A-2006-196277). According to this battery pack, it is possible to drain the water, which has been entered into the housing case, to the outside of the housing case from the drain hole, and therefore, it is possible to avoid the soaking of the lead plates in water, so that electricity charged in the battery cells may not leak.
Incidentally, in order to improve the drainage effect described above, it has been considered to provide a plurality of the drain holes formed at the bottom portion of the housing case.
However, if the plurality of drain holes are merely formed at the bottom portion of the housing case, conversely, water or dust may easily enter into the housing case from the drain holes. For this reason, it is preferable that the number of the drain holes is as small as possible, while the drainage effect described above is enhanced.
It is an object of the invention to provide a battery pack that is configured to be capable of being mounted on a tool body of an electric tool as a power source of the electric tool, can efficiently drain water having been introduced into a housing case to the outside of the housing case so as to prevent the leakage of the electricity charged in battery cells, and can make the number of drain holes be as small as possible.